The field of the invention is that of sensors for detecting the presence or concentration of particular chemical or biological species and the invention relates more particularly to a novel and improved sensor utilizing an optical fiber.
Certain known fiber optic chemical sensors as shown in U.S. Pat. Nos. 4,824,206 and 4,846,548 use an optical fiber having a core of light-transmitting material and a cladding of relatively lower refractive index than the core. The fiber receives light within one end of its core and transmits the light along the length of the core by total internal reflection from an interface located within the fiber between the fiber core and cladding. A light sensor receives the light at the opposite end of the core and provides an electrical signal corresponding to the amount of light transmitted by the fiber. The cladding is formed of a material which reacts when contacted by a particular chemical or biological species to produce a measurable change in light transmission by the fiber, whereby a change in the signal provided by the detector is representative of the presence or concentration of the species in contact with the cladding. In one known sensor, the light source and detector comprise light-emitting and detecting diodes provided in a common semiconductor body and the optical fiber is fitted into a channel provided in the body to conduct light from the source to the detector. In such known devices it is difficult to furnish and receive light to and from the fiber in a consistent manner and it is difficult to arrange the device to monitor a zone for the presence of the particular chemical or biological species.